A light-emitting device using a light-emitting diode (LED) is composed principally of a combination of an LED chip as an excitation light source and a phosphor. Various emission colors may be realized by the combination.
The combination of a blue LED chip which emits blue light and the phosphor is used, for example, in a white LED light-emitting device which emits white light. A yellow phosphor complementary to blue color is principally used as the phosphor. In addition, a three wavelength type white LED formed of the combination of the blue LED chip which emits blue light, a green phosphor, and a red phosphor and the like is developed.
When a wavelength of the blue light being the excitation light source changes due to a temperature, a driving current amount, manufacturing variation and the like, balance of yellow light, green light, or red light emitted by the phosphors is lost and chromaticity change might occur. In this case, a problem of “color shift” that desired chromaticity cannot be obtained occurs.
Especially, in a light-adjusting light-emitting device in which intensity of the white light is changed by change in emission intensity of the blue LED, an emission wavelength of the blue LED changes due to change in driving current, so that the problem of “color shift” is remarkable.